Former President Bill Clinton appears at a campaign stop for his his wife, Democratic presidential candidate Hillary Clinton, in front of the Buttonwood Park warming house in New Bedford, Massachusetts on Tuesday. | PETER PEREIRA / STANDARD TIMES VIA AP

WASHINGTON – Republican Donald Trump and Democrat Hillary Clinton pressed for sweeping victories on Super Tuesday, the biggest day in the primary campaign and one that could distance them from their party rivals and move them closer to a November election showdown.

Trump, the brash billionaire and reality TV star, has stunned the Republican political establishment by winning three of the first four contests, seizing on the anxieties of voters angry at Washington and worried about terrorism, immigration and an uncertain economy. Using simple terms, and often coarse language, he has soared to the top of polls with his pledge to “make America great again.”

Republican officials, fearing a Trump sweep, have been lashing out at his temperament and command of the issues in the hours before voting began.

“You’ve got a con man and a bully who is moving forward with great speed to grab the party’s mantle to be its standard bearer,” Norm Coleman, a former senator who backs Marco Rubio, said in an interview with The Associated Press. “That’s almost incomprehensible.”

Clinton, once seen as the all-but-inevitable Democratic nominee, has contended with an unexpectedly strong challenge from Bernie Sanders, a Vermont senator and self-described democratic socialist. But Clinton, like Trump, has also won three of the first four races, and a landslide victory in South Carolina on Saturday bodes well for prospects in important Southern states Tuesday due to her overwhelming support among black voters.

Elections were being held Tuesday in 12 of the 50 U.S. states. Candidates vie to win delegates who will vote for them at the parties’ conventions in July. For Republicans, 595 delegates were at stake, nearly half of the 1,237 needed for the nomination. Democrats were allocating 865, delegates more than one-third of the 2,383 needed to become the nominee.

Tuesday’s vote was critical for the two leading Republicans vying to be Trump’s main challenger: Ted Cruz, a firebrand conservative senator from Texas, and Rubio, a Florida senator who has become the favorite of much of the Republican establishment.

Both senators have launched furious verbal attacks on Trump in recent days, but some in the party establishment fear the anti-Trump campaign has come too late.

Cruz once saw the Southern states that vote Tuesday as his opportunity to stake his claim to the nomination, given their large evangelical Christian populations, only to see Trump pick up a sizable segment of evangelicals. Now the Cruz campaign’s future hinges on a victory in his home state of Texas, the biggest prize up for grabs.

Rubio’s goal is even more modest. He’s seeking to stay competitive in the delegate count and hoping to pull off a win in his home state of Florida on March 15.

Even before the results started flowing in, Trump was calling for Rubio to quit the race if he didn’t win anywhere on Tuesday.

“He has to get out,” he told Fox News. “He hasn’t won anything.”

Ohio Gov. John Kasich and retired neurosurgeon Ben Carson remain in the race, but neither is expected to be a major factor on Tuesday.

Republicans spent months largely letting Trump go unchallenged, wrongly assuming that his populist appeal with voters would fizzle. Now Republican leaders are divided between those who pledge to fall in line behind him if he wins their party’s nomination and others who insist they can never back him.

The worries among Republicans appeared to grow after Trump briefly refused to disavow the apparent support of former Ku Klux Klan leader David Duke during a television interview. Trump later said he had not understood the TV interviewer who had first raised the question about, and he did repudiate him.

The disarray among Republicans comes as Clinton appears to be tightening her grip on the Democratic race. She has increasingly turned her attention away from Sanders and on to Trump, casting herself as a civil alternative to the insults and bullying that have consumed the Republican race.

“What we can’t let happen is the scapegoating, the flaming, the finger pointing that is going on the Republican side,” she told voters in Massachusetts. “It really undermines our fabric as a nation.”

Sanders, who has energized young voters with his call for a political revolution, was seeking to stay close to Clinton in the South and pick up victories in other states including Minnesota and his home state of Vermont. But Sanders faces tough questions about whether he can rally minorities who are core Democratic voters.

Democrats were voting in 11 states and American Samoa; Republicans were voting in 11 states..

States holding voting contests in both parties are Alabama, Arkansas, Georgia, Massachusetts, Minnesota, Oklahoma, Tennessee, Texas, Vermont and Virginia. Republicans also vote in Alaska and Democrats in Colorado. Democrats also have a contest in American Samoa and for Democrats Abroad.